Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.32	6.114%	$55.5188	$55.52	$55.50	$55.50
Purchase #2	$80.56	11.466%	$89.797	$89.80	$89.80	$89.80
Purchase #3	$161.82	11.496%	$180.4228	$180.42	$180.40	$180.40
Purchase #4	$242.99	10.154%	$267.6632	$267.66	$267.65	$267.70
Purchase #5	$125.50	12.360%	$141.0118	$141.01	$141.00	$141.00
Purchase #6	$69.61	5.358%	$73.3397	$73.34	$73.35	$73.30
Purchase #7	$105.53	3.832%	$109.5739	$109.57	$109.55	$109.60
7 purchase totals =	$838.33		$917.3272	$917.32	$917.25	$917.30